Multicolor printing



y 1938- A. c. DOBROTH. .JR' 2,117,546

MULTICQLOR PRINTING Filed Oct. 3, 1936 A/berf C. DobrorhJn Patented May 17, 1938 UNITED STATES PATENT OFFICE Application October 3,

6 Claims.

This invention relates to the art of sheet-fed rotary machine printing and has Particular application to the printing of superimposed colored inks upon various types of paper. Heretofore,

this method of printing has been adapted pri marily to the production of commercial prints in large quantities or in job lots and as a result the quality of the resulting work has been subordinated to the necessities of rapid printing.

10 While'the three, four and five color printing methods of the present, as exemplified by contemporary magazine covers, are largely conducted upon sheet-fed rotary machines, it is found that certain disadvantages are present.

In order to secure a quality type of printed product the characteristics of the paper, the ink and the printing press must each be considered. As a result of the demands for quantity production the presses are designed and operated for maximum speeds and the ink frequently is unable to set or to partially dry between successive impressions upon the paper. This then gives rise to a lack of brilliancy and loss of detail in the final product due to the middle tones of color becoming too light or to the light tones of color becoming flattened or running together.

This problem, moreover, is accentuated by the fact that the conventional paper used for magazine covers or the like is usually hard-sized. As a consequence, the paper tends to take the ink on the raised portions of the paper grain, while the minute depressions in the paper surface remain more or less bare thus giving rise to a grainy or unsound impression. In order to avoid this, a slight dilution of the gravure ink is sometimes made but this expedient gives rise to a more or less mottled or granular effect particularly in the darker tones. When the printed paper is then examined under a microscope it 40 is found that dots constituting the image become indistinguishable in the darker middle tones and shadows because the ink has piled up irregularly and given a grainy effect.

Various ink drying expedients have been employed upon sheet-fed rotary presses to overcome these difficulties, but have required the use of complicated apparatus and have not met with notable success. In printing by means of web rotary presses the above mentioned problem has not been presented due to the fact that a compact machine with closely spaced printing rolls is not employed in this process. Furthermore, since the exact register of color required for precision multicolor printing in quantities can be secured practically only upon a sheet-fed rotary 1936, Serial No. 103,863 (01. 101-174) press of campact construction, it follows that the problem thus presented is peculiar only to this specific process of printing.

The present invention provides a solution to these problems and has as an object the teaching of a method for printing multicolor impressions with a sheet-fed rotary apparatus and characterized by the fidelity of color gradation upon the resulting product. i

A second object is the teaching of a method for rapidly printing multicolor impressions upon paper while insuring well rendered high-lights" and shadows in the resulting product.

Another object is the provision of sheet-fed rotary printing apparatus adapted to print multicolor sheets of superior color gradation without reducing the normal capacity of the apparatus.

A further object is the provision of improved printing apparatus capable of being adapted to existing sheet-fed rotary printing apparatus.

Other objects and advantages of the invention will become more apparent when considered in conjunction with the accompanying drawing in which the figure illustrates one diagrammatical form of apparatus capable of carrying out the invention.

As the description proceeds it will become evident that the invention is adapted for conducting the improved printing process either upon a special press designed primarily in accordance with this teaching or upon a conventional installed press to which the improved apparatus herein disclosed may be applied. Consequently, it is to be expressly understood that the accompanying drawing merely shows on form which the apparatus may assume and that the invention is not to be limited solely to that particular design of printing press.

Referring now to the drawing, a substantial support means I has housed therein a large immore fully disclosed hereinafter, this function of an impression roll in the printing process is of great importance in producing quality work and the present invention has as an important object the teaching of a means for independently regulating the pressures applied to the sheets at the critical printing steps.

Housed within the support means adjacent the upper portion thereof is a rotatable guide 3 supporting a conveyor means 4 and 5 adapted to remove the printed sheets from the press after the final printing impression has been received.

A plurality of plate cylinders 6, 1, 8 and 9, each of which is adapted to place a different color ink upon the sheets of paper may be housed in the support means 1. Each of these cylinders cooperates with the impression cylinder 2 and is adapted to print upon the paper sheets a predetermined color ink with a gradation of color according to the plate structure which they carry.

In certain apparatus now available the plate cylinder adapted to print the initial color is located a short distance from cylinder 9 in a location comparable to the locations of cylinders 6, .1, 8 and 9 which are shown as being adjacent the impression cylinder in this usual type of apparatus. The unprinted sheets of paper entering the press by means of a conveyor mechanism having an intake cylinder are secured to impression cylinder similar to that shown at 2 by holding means or grippers and immediately pass under the several plate cylinders in rapid succession meanwhile receiving the several superimposed color ink impressions.

Due to the fact that such an apparatus is compact and can be operated at high speeds with consequent large quantity production and at the same time give a superior register of impressions, numerous disadvantages of the apparatus and meth- 0d of printing have been overlooked.

As before stated, the hard-sized paper customarily printed on sheet-fed rotary presses tends to take ink chiefly upon the raised portions of the paper fiber. In order to impress the ink rapidly into the pores of the paper, sufficient pressure has to be exerted by the initial plate cylinder to make etched designs of the plate sufficiently clear. This pressure, if excessive, forces the paper sheet into the tympan sheet and causes disagreeable raised portions on the opposite side of the sheet being printed which in turn results in a problem when that side of the sheet is later printed. Since the sheet therefore assumes an irregular surface, each of the succeeding plate cylinders 9, 8, I and 6 must be adjusted to provide a pressure commensurate with the pressure exerted by the initial plate cylinder so as to lay the superimposed ink in its proper place upon the initial ink.

Consequently when all of the plate cylinders cooperate with a single impression cylinder, the superimposed ink impressions tend to pile up on each other With excessive pressure and intermix thus giving rise to a muddy color in the final product.

This problem, moreover, is enhanced by the fact that the ink does not have suflicient time to set or to dry partially between the first and succeeding impressions. With a compact sheet-fed rotary press running at a cyclic rate of 5000 sheets per hour it is estimated that only one-fifth of a second or less elapses between the initial impression and the first succeeding impression. The recourse to auxiliary ink drying equipment by itself has not been wholly satisfactory due partially to the fact that the use of a single impression roll requires the second and succeeding plate cylinders to exert excessive pressures upon the first ink impression.

It has been found that the initial ink impression,

which customarily is the yellow impression, plays an extremely important part in the quality of the resulting work and that unless a thorough impregnation of the paper with fidelity of plate etching is made at this critical stage the quality of the work invariably suffers. If the initial impression is properly made and at the same time the ink can set sufiiciently and the pressures of succeeding impressions are properly adjusted, a remarkable brilliancy and. clarity of detail can be obtained in the final product. i

The present invention provides a solution to these problems and as shown in the drawing a housing It] adapted to support a portion of the printing apparatus is located adjacent the main support means I and is afiixed thereto by any suitable securing arrangement.

A conveyor means ll brings successive sheets of paper I2 to the usual intake cylinder l3 which directs the sheet to an auxiliary impression cylinder l5 spaced from and independent of themain impression cylinder 2. Cooperating with the impression cylinder I5 is the initial plate cylinder 94 which impresses the initial color upon the paper sheet. The sheet thus printed is transferred from the auxiliary impression cylinder to the main impression cylinder by means of a transfer cylinder 16.

Due to the arrangement thus provided the sheet travels a substantially greater distance, in comparison with present apparatus, from the first to the second plate cylinders and a commensurately greater time elapses between these print ings with the result that the initial ink has sufiicient time to set normally and to creep into the microscopic pores of the paper sheet before having other ink superimposed upon it. This factor obviates the necessity for using excessive pressure upon the initial plate cylinder in order to force the ink rapidly into the paper and at the same time results in a sheet having a primer coat of properly distributed ink. The successive sheets then receive the second ink impression from cylinder 9 and the remaining ink impressions from cylinders 8, I and 6.

Since the initial color impression thus applied has an opportunity to set upon the paper, the succeeding impressions may be made in rapid succession and with closely regulated pressures.

As a consequence, very light frictional contacts eliminated. Furthermore, the delicate gradation 5 of color required for well rendered high lights, shadows and curved surfaces is also secured since the etched plates on the later printing cylinders are enabled to lay their ink with as light a pressure as is consistent with a sound impression.

While the structure as shown is designed to print five colors it will be apparent that a smaller or larger number of color plate cylinders may be provided without departing from the teachings of the invention.

It will be noted that by following this teaching no loss in capacity of the apparatus is sustained. The successive sheets pass through'the press with the same speed as before but travel through a longer path between the first and second plate cylinders. The location of housing 10 provides access to cylinders l4 and 9 for the usual inking carriage and housing and necessitates no change in design of the conventional apparatus in this regard.

Lit

In the event that additional auxiliary drying of the initial ink impression is desired, it is con templated that any suitable drying apparatus as indicated diagrammatically at !1 may be installed without departing from the teachings of the invention.

Since the many advantages derived from this improved process result primarily from the use of an initial printing step which is separate from the remaining printing steps, it is obvious that this initial printing step becomes the critical phase of the entire process. Numerous changes, therefore, in the apparatus designed to carry out this step will occur to the person skilled in the art. The location of cylinder !4 so as to secure the requisite path of movement of the sheet before reaching cylinder 9 may be subjected to wide variations. The adjustment of printing pressure exerted by the plates of cylinder [4 against the paper sheet will likewise be subject to variation depending upon the texture of the paper and the nature of the ink being used.

Since these changes may readily be employed without departing from the essentials of the invention, it is with the intention of including such changes in the above disclosure as will occur to one skilled in the art that,

I claim:

1. The process of printing three or more superimposed color impressions upon separate sheets of paper moving at a substantially constant rate of speed comprising, printing an initial color impression upon a sheet at a point in its path of movement relatively distant from the second color impression point and at a correspondingly large interval of time, printing a second color impression upon the initial color impression of the same sheet whereby the interval of time elapsing between the first and second impressions is sufilcient to permit the initial ink to set and to allow the second ink impression to form a welldefined color gradation thereupon and then printing a third color impression upon the previous impressions and at a point in the path of movement of the sheet relatively near to the second color impression point and at a correspondingly small interval of time.

2. In the printing of three or more superimposed color impressions upon each of a series of consecutive sheets of paper moving at a substantially constant rate of speed, the method of forming Well-defined color gradations of the several color impressions comprising, impregnating the paper with an initial color ink at a point in its path of movement relatively distant from the second color impression point and at a correspondingly large interval of time in order to provide a partially dry primer coat on the moving sheets of paper prior to adding a different color impression, printing a second color impression upon the partially dry initial impression and then printing succeeding superimposed color impressions at points in the path of movement of the paper relatively close to the second color impression point.

3. The improvement in the art of sheet-fed rotary machine multicolor printing comprising, printing an initial color at a point in path of movement of the sheet relatively distant from the second color impression point by means of an initial pressure insuihcient to form substantial depressions in the paper sheet, moving the sheet through a time interval between the initial and next' succeeding inking operations suflicient to permit the initial ink to impregnate the pores of the paper and to set upon the paper, applying a second and different color ink upon the initial ink by means of a pressure independent of the initial printing pressure and then applying one or more additional colors to the inked sheet at points spaced relatively close to the second inking point in the path of movement of the sheets.

4. The improvement in the art of sheet-fed rotary machine multicolor printing comprising, printing an initial color at a point in path of movement of the sheet relatively distant from the second inking point by means of an initial pressure capable of depositing the initial ink in conformity to the plate etching but incapable of forming substantial depressions in the paper sheet, moving the sheet through a space between the initial and next succeeding inking points sufiicient to permit the paper to take up the ink in the form of a primer coat, superimposing a difierent color ink upon the primer coat by means of a relatively light pressure independent of the initial printing pressure, whereby clarity of detail may be obtained in the printed product and then superimposing a third color ink upon the previously inked sheet at a point in its path of movement relatively close to the second inking point.

5. A rotary printing apparatus adapted to print three or more superimposed color impressions upon separate sheets of paper moving at a substantially constant rate of speed comprising, a main impression cylinder, a plurality of color plate cylinders spaced at approximately equal intervals and at small distances apart and cooperating with the main impression cylinder, a separate impression cylinder spaced at a substantially large distance from the main impression cylinder, an initial color cylinder cooperating with the spaced impression cylinder, means to transfer the sheets of paper from the spaced impression cylinder to the main impression cylinder, means to feed the unprinted sheets of paper to the spaced impression cylinder and means to remove the printed sheets of paper from the main impression cylinder.

6. A rotary printing apparatus adapted to print three or more superimposed color impressions upon separate sheets of paper moving at a substantially constant rate of speed comprising, a main impression cylinder, a plurality of color plate cylinders spaced at approximately equal intervals and at small distances apart and cooperating with the main impression cylinder, a sep arate impression cylinder spaced at a substantially large distance from the main impression cylinder, an initial color cylinder cooperating with the spaced impression cylinder, means to transfer the sheets of paper from the spaced impression cylinder to the main impression cylinder, auxiliary drying means located adjacent the path of the paper sheet intermediate the im pression cylinders, means. to feed the unprinted sheets of paper to the spaced impression cylinder and means to remove the printed sheets of paper from the main impression cylinder.

ALBERT C. DOBROTH, JR. 

